Self-assembled coordination cage as a molecular flask*

Cavity-directed chemical transformations represent one of the most important features in 3-D host chemistry, yet they are unexplored as synthetic receptors. We are developing such functions with the large cavity of self-assembled cages, particularly an M6L4-type cage. The photodimerization of olefins within this cage shows remarkable rate enhancement, perfect regioand stereoselection, and high pairwise selection (when two different olefins are used) giving only the cross [2+2] adduct. Another intriguing property of the cavity is the stabilization of labile molecules by encapsulation. We succeeded in trapping labile molecules by in situ preparation from small components coming through small portals of the cage. For example, hydrolysis and condensation of PhSi(OMe)3, which ordinarily provides a sophisticated Si–O 3-D network (so-called sol-gel condensation), selectively gave a cyclic trimer, [PhSi(OH)O]3, in a “ship-in-a-bottle” fashion. Cavity-sensitized photochemical oxidation of alkanes within the cage is also discussed.